install script doesn't work correctly with ubuntu

`install.sh` only checks for linux, but it should detect debian and download that release.

```sh
curl -fsSL https://wush.dev/install.sh | sh
```

```sh
Downloading wush from https://github.com/coder/wush/releases/download/v0.2.1/wush_0.2.1_linux_arm64.tar.gz...
Extracting wush...
wush installed successfully!
```

```sh
wush serve
bash: /usr/local/bin/wush: Operation not permitted
```

The container is on a docker host on an Mac M3

```sh
uname -m
aarch64
```

Thus it tries to bring down `..._linux_arm64.tar.gz`

I manually wget `...linux_amd64.tar.gz` or `...linux_amd64.deb` and `wush` works